The present invention relates generally to the field of batteries (e.g., lead-acid batteries such as automotive starting, lighting, and ignition (SLI) batteries; industrial batteries; commercial batteries; and marine batteries). More specifically, the present invention relates to materials for use in active materials for batteries and methods of making such materials.
Positive and negative plates or grids utilized in lead-acid batteries are made of lead or a lead alloy, and include a plurality of wires coupled to a plurality of nodes (e.g., a battery plate may include a frame comprising four sides with a lug or current collector extending from one of the sides and a network of wires or grid elements interconnected with a plurality of nodes).
At least a portion of the positive grids or plates have a material (e.g., a paste) applied thereto. The paste typically comprises lead oxide (PbO). The active material may also include one or both of tetrabasic lead sulfate (4PbO.PbSO4) (often abbreviated as “4BS”) and tribasic lead sulfate (3PbO.PbSO4.H2O) (often abbreviated as “3BS”). According to an exemplary embodiment, an active material may comprise approximately 40% PbO and 60% 4BS. According to other exemplary embodiments, the active material may have a different composition (e.g., the active material may include between approximately 10% and 100% 4BS, etc.). The tetrabasic lead sulfate and tribasic lead sulfate may be provided in the form of individual crystals that are mixed into the lead oxide paste material. According to an exemplary embodiment, tetrabasic lead sulfate and tribasic lead sulfate may be provided by adding acid to a paste mix under appropriate mixing and plate curing conditions.
The positive plates having paste applied thereto are cured or dried to remove excess liquid in the paste and assembled into a battery (e.g., positive and negative plates are provided with a separator between them in a battery container, after which acid (e.g., sulfuric acid) is introduced into the battery). During curing, the tetrabasic lead sulfate and/or tribasic lead sulfate crystals grow or increase in size.
During battery formation (e.g., providing an initial charge to the battery), the components of the paste are converted to an active material such as lead dioxide (PbO2) on the positive plates and sponge lead (Pb) on the negative plates. According to an exemplary embodiment, a sulfation reaction proceeds as acid is added to the battery according to the formula:PbO+H2SO4=PbSO4+H2O
During formation, according to an exemplary embodiment, the reactions at the positive and negative plates proceed according to the following formulae: